Regex: support the dot

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

test/Regex.java

@@ -33,5 +33,7 @@ public class Regex {
     expectNoMatch("a(bb)?a", "abbba");
     expectNoMatch("a(bb)?a", "abbaa");
     expectGroups("a(a*?)(a?)(a??)(a+)(a*)a", "aaaaaa", "", "a", "", "aaa", "");
+    expectMatch("...", "abc");
+    expectNoMatch(".", "\n");
   }
 }

test/regex/Compiler.java

@@ -141,6 +141,9 @@ class Compiler implements PikeVMOpcodes {
         continue;
       }
       switch (c) {
+      case '.':
+        current.push(DOT);
+        continue;
       case '?':
         current.push(new QuestionMark(current.pop()));
         break;